JP2000224877A - Speed controlling method of switched reluctance motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make controllable the speed of an SR motor through using cheap switching elements, by performing a pulse width modulation control of its speed when it is in a transient state and a dowel control of its speed when it is in a stationary state to decrease the switching frequencies of the switching transistors of its inverter. SOLUTION: A speed sensing portion of a switched reluctance motor receives the signal inputted from its speed sensor to output a sensed pulse signal ps. Its speed controlling portion compares its speed with a preset reference speed based on the sensed pulse signal ps. When it is in a transient state, a pulse width modulation control for increasing progrssively the duty factor of its switching signal pulse is continued to increase its speed progressively. On the other hand, when it is in a stationary state, its speed controlling portion interrupts the pulse width modulation control of its speed to perform a dwell control wherein the superordinate first to third switching transistors of the first to sixth ones of its inverter are brought into turn-on states.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a switched reluctance motor (hereinafter referred to as SR).
More specifically, the present invention relates to a speed control method for an SR motor that can be applied to a load having a large mechanical inertia which is a load having a small instantaneous response.

[0002]

2. Description of the Related Art Generally, as a speed control method of an SR motor, a pulse width modulation (PW) is used.
The control method and the current control method are widely used. In the PWM control method, the pulse width of the switching transistor is modulated based on the pulse corresponding to the output value of the speed detection sensor for speed detection. In the current control method, a current hysteresis band (hysteresis band (hysteresis band) is applied within a switching section in which a switching transistor is switched.
The width of the steresis band is set, and the switching transistor is switched so that the current applied to the motor winding is present inside the hysteresis band, thereby preventing a phenomenon that an overcurrent flows through the motor winding.

[0003] In a conventional three-phase SR motor,
As shown in FIG. 4, it was configured to include a rotor 10, a stator 20, and windings La, Lb, and Lc wound around the stator 20. In the conventional three-phase SR motor speed control circuit configured as described above, as shown in FIG.
An inverter 21 including first to sixth switching transistors Q1 to Q6, diodes D1 to D6, and a DC capacitor C connected in parallel to the power supply side, and the rotation of the motor rotor 10 are detected to detect a signal. A detection sensor 22, which outputs a detection pulse signal ps by determining the position of the rotor based on the signal, and receives the detection pulse signal ps,
A speed control unit 24 that outputs a plurality of switching signals cs1 to cs6 to each gate of the first to sixth switching transistors Q1 to Q6 of the inverter 21 so as to rotate the rotor to a desired speed, respectively. The upper three switching transistors Q1 to Q3 were connected in series with the lower three switching transistors Q4 to Q6 and the motor windings La, Lb, and Lc.

[0004] The operation of the conventional three-phase SR motor thus configured will be described below with reference to the drawings. Fig. 6 shows the first, fourth, and three-phase SR motors controlled by the PWM method.
FIG. 10 is a waveform diagram showing the switching signals cs1, cs4 applied to the gates of the switching transistors Q1, Q4, respectively, and the current ia applied to the A-phase winding La by the switching signals cs1, cs4, as shown in FIG. In addition, the speed detection unit 23 determines the current position of the rotor 10 based on a signal input from the detection sensor 22, and every time the rotor 10 rotates a predetermined angle, for example, a circumferential angle of 60 °, , And outputs the detection pulse signals ps1 and ps2 to the speed control unit 24, respectively.

Next, the speed control unit 24 receives the first detection pulse signal ps1, outputs a high-level fourth switching signal cs4 to the fourth switching transistor Q4, and outputs a high-level signal to the first switching transistor Q1. And outputs a modulated first switching signal cs1 having a pulse width in which the low level is alternately repeated. Then,
4 By the switching signal cs4, the fourth switching transistor Q4 is maintained in the ON state, and by the first switching signal cs1, the first switching transistor Q1 is
The on / off state is alternately repeated.

In this case, the pattern of the current ia flowing through the A-phase winding La has a sawtooth waveform that gradually increases as shown in FIG. And the rotor 10 continuously rotates,
After the first detection pulse signal ps1 has been generated, when it rotates by a circumferential angle of 60 °, the speed detection unit 23 outputs a second detection pulse signal ps2 to the speed control unit 24, and the speed control unit 24
Sets the first and fourth switching signals c1 and cs4 to low level and sets the first and fourth switching transistors Q1 and Q4
Is turned off, and the current ia flowing through the A-phase winding La is reduced to '0'.

[0007] Thereafter, the speed control unit 24 is operated by the second and fifth speed control units.
The switching signals cs2 and cs5 are output to a high level, and a current flows through the B-phase winding Lb (not shown). In this case, the speed of the motor can be increased by increasing the pulse duty of the first switching signal cs1. That is, while the fourth switching transistor Q4 is turned on, the average time during which the first switching transistor Q1 is turned on is increased, so that the rising section of the A-phase current ia is extended and the falling section is reduced, The speed of the motor is increased.

On the other hand, when the load increases, the speed of the SR motor decreases in proportion to the load, and the first detection pulse signal ps1
The interval T between the second detection pulse signal ps2 and the second detection pulse signal ps2 becomes longer. That is, the interval T increases, the time during which the fourth switching transistor Q4 is turned on increases, and the
1 Since the switching transistor Q1 is switched for a longer time, the A-phase current ia is increased.

When the speed of the motor is significantly reduced in accordance with a sudden increase in the load, the section T sharply increases. This means that the switching section T of the first switching transistor Q1 increases. At this time, the A-phase current ia rapidly increases, and the rated current (rated curren
t) may be exceeded. Therefore, in order to prevent the motor from being damaged due to the occurrence of overcurrent, a separate current protection circuit that can cut off the overcurrent flowing through the system is required, but such a current protection circuit has a circuit configuration. There is a problem that it is complicated and the cost of the system increases.

In order to prevent the overcurrent from flowing, a predetermined value of the current hysteresis bandwidth is set in advance, and the current is controlled so that the current value does not deviate from the hysteresis bandwidth. FIG. 7 shows that the first and fourth switching transistors Q are used to control the current of a conventional three-phase SR motor.
1, switching signal c applied to the gate of Q4 respectively
s1, cs4 and their switching signals cs1, cs4
FIG. 8 is a waveform diagram showing currents ia applied to the A-phase winding La, respectively, and as shown in FIG. 7, the first detection pulse signal ps
When 1 is generated, the speed control unit 24 outputs the first and fourth switching signals cs1 and cs4 to a high level,
Although the phase current ia is increased, when the value of the phase A current ia exceeds the current hysteresis band, the speed control unit 24
1 Turn off the switching transistor Q1 to reduce the A-phase current ia.

Thereafter, when the value of the A-phase current ia becomes smaller than the current hysteresis bandwidth, the speed controller 24
Turns on the first switching transistor Q1. This process is repeated until the second detection pulse signal ps2 is generated. Thus, the A-phase current ia
Is controlled so as not to exceed a preset hysteresis bandwidth, thereby preventing a phenomenon in which an overcurrent flows through the A-phase winding La.

[0012]

[Problems to be solved by the invention] However, the conventional three-phase SR
In the motor speed control method, a high switching frequency of about 15 to 20 kHz is used in order to prevent noise generated at the time of switching of the switching transistor. When such high-speed switching is performed, an insulated gate bipolar transistor is used. (Hereinafter referred to as an IGBT) or an expensive power switching element such as a field effect transistor (hereinafter referred to as an FET) is indispensable, and there is an inconvenience that switching loss increases.

An object of the present invention is to provide a speed control method of an SR motor that can control the speed of an SR motor using a general low-cost switching element without using a high-speed current switching element. is there. Another object of the present invention is to provide a speed control of an SR motor capable of switching a specific switching transistor within a corresponding switching interval for a predetermined time when the SR motor operates in a steady state. It is to provide a method.

[0014]

In order to achieve the above object, a speed control method for an SR motor according to the present invention is a speed control method for an SR motor using a load having a large mechanical inertia. After the SR motor is started, the PWM
Performing the control to increase the speed of the motor; and
Based on the speed of the motor, a step of determining whether the SR motor is in a steady state, and, as a result of the determination, when the SR motor is in a steady state, or when approaching a steady state, a preset time, the inverter And controlling the current flowing through the windings to be constant irrespective of the change in the load of the motor.

In this case, the load of the SR motor is
Loads with low instantaneous responsiveness, which are loads with high mechanical inertia, are limited because, when a load with low mechanical inertia is used, the speed changes drastically, and the turn-on state is maintained for a certain period of time. This is because it is difficult to maintain and perform accurate control.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. The speed control circuit of the SR motor according to the present invention has substantially the same configuration as the conventional one, as shown in FIG. The speed control method of the SR motor according to the present invention configured as described above will be described with reference to FIG.

First, after the motor is started in the initial stage, the PWM
Although control of (pulse width modulation) is performed (S101), such a control operation is continuously performed during a transient state in which the speed of the motor is rapidly increased. At this time, the speed detection unit 23 receives the signal input from the detection sensor 22, outputs a detection pulse signal ps, and the speed control unit 24
It is determined whether the motor speed is higher than a preset reference speed based on the detection pulse signal ps (S102).

At this time, the reference speed value is a speed value for distinguishing whether the speed of the motor is in a transient state or a steady state. Next, if it is determined in step S102 that the motor is in a transient state, the control of the PWM for gradually increasing the duty of the pulse of the switching signal is continued to gradually increase the speed of the motor.

If it is determined that the motor is in a steady state, the speed control unit 24 stops the PWM control. FIG. 2 is a graph showing a speed control pattern of the SR motor according to the present invention. As shown, the first section (T1) is in an excessive state where the motor speed is rapidly increased after the initial startup. The second section (T2) is a normal state in which the motor speed becomes constant to some extent after the transient state has elapsed. In the steady state T2, the speed control unit 24
Inverter first to sixth switching transistors Q1 to
Of the Q6, the top three switching transistors Q1 to Q1
Q3 is controlled so as to be sequentially turned on for a predetermined time (S103, S104).

Such a control operation has the opposite concept of switching the switching signal to a high frequency when the PWM control is performed. In the present invention, for the sake of convenience of description, "dwell" is used. The control will be described. That is, during PWM control, as shown in FIG. 6, the switching signal cs1 is switched to a high frequency in the section T, but during dwell control, the switching signal cs1 is switched.
1 is kept on for a predetermined time, and the switching signal cs4 is also kept on as in the case of the PWM control.

FIGS. 3 (a) to 3 (c) show that when the dwell control of the SR motor according to the present invention is performed, the upper level is detected by the detection pulse signal ps.
In the waveform diagram of the switching signals cs1 to cs3 respectively applied to the gates of the three switching transistors Q1 to Q3, the remaining lower three switching transistors Q4 to Q6
Maintain an ON state during a period in which the upper three switching transistors Q1 to Q3, which are connected in series, are turned on, and the operation is the same as in the related art.

The pulse width Tona of the switching signal cs1 at the time of low speed operation shown in FIG. 3A is shorter than the pulse width Tonb of the switching signal cs1 at the time of medium speed operation shown in FIG. Switching signal cs1 during high-speed operation shown in Fig. 3 (c)
The pulse width Tonc is the switching signal cs1 during medium speed operation.
The remaining switching signal cs longer than the pulse width Tonb
2, cs3 is the same.

The pulse width of such a switching signal
(Tona, Tonb, Tonc) is a concept for time,
The pulse width of these switching signals (Tona, Tonb, Ton
c) That is, as the on-time increases, the current flowing through the windings La, Lb, Lc of the corresponding motor increases, and the rotor 1
0 is rotated faster. Further, the speed control unit 24 has a pulse width of a switching signal corresponding to a desired rotation speed.
The ON time (Tona, Tonb, Tonc) of the switching signal (Tona, Tonb, Tonc) is stored in the table.

If it is determined in step S102 that the motor is in a steady state, the speed control unit 24
Stops the PWM control, determines the current speed of the motor based on the detection pulse signal ps, and takes into consideration the current speed and the speed to be controlled, the pulse width of the switching signals cs1 to cs3.
(Tona, Tonb, Tonc) are respectively determined (S103), and the switching signals cs1, cs2, cs3 having the pulse widths (Tona, Tonb, Tonc) are sequentially applied to the first to third switching transistors Q1 to Q3 ( S104).

In this case, the speed control unit 24 receives the first detection pulse signal ps1 shown in FIG.
Output switching signal cs1 with Tona, pulse width
Output a switching signal cs4 having T. Therefore,
The first switching transistor Q1 is turned on during the on-time Tona, and the fourth switching transistor Q4 connected in series to the first switching transistor Q1 via the A-phase winding La is turned on for the time T by the switching signal cs4. Current flows through the A-phase winding La during the on-time Tona, and after the on-time Tona elapses,
The current flowing through the A-phase winding La is gradually reduced.

After a predetermined time T has elapsed after the first detection pulse signal ps1 has been input, the second detection pulse signal ps1
2 is input, the speed detection unit 24 outputs the pulse width Tona
To output a switching signal cs5 having a pulse width of T time.
A current flows through the phase winding La during the on-time Tona. By repeating such a process, the desired motor speed can be controlled.

On the other hand, if the speed of the motor suddenly decreases in accordance with the sudden increase in the load, the period T shown in FIGS.
Increase, the turn-on interval T of the switching signals cs4 to cs6 becomes longer, and the lower three switching transistors Q
4 ~ Q6 turn-on time becomes longer. However, since the on-time Tona of the switching signals cs1 to cs3 is set in advance, the on-time Tona of the first to third switching transistors Q1 to Q3 does not change even if the load is suddenly increased. Since there is no change in the amount of current flowing through each of the windings La, Lb, and Lc, even if the load is rapidly increased and the speed of the motor is rapidly reduced, no overcurrent flows through the motor windings and the switching elements. The motor winding and the switching element can be protected.

As described above, in the present invention, since the on-time of the switching signal is set in advance, a constant current is supplied to the motor irrespective of the sudden increase in the load, and the sudden increase in the load causes The phenomenon that the motor is damaged can be prevented. Next, when the speed control of the motor is reduced due to the overload, the section for applying power to the motor is reduced, and the amount of power applied to the motor is reduced. Further, when the speed is reduced, the speed control unit 24 outputs a switching signal.
Stop driving the motor without outputting cs1 to cs6 (S10
Five). In this case, the determination of the overload is performed in consideration of the specifications of the motor.

As described above, for convenience of explanation, the first
Within the interval T from when the detection pulse signal ps1 is output to when the second detection pulse signal ps2 is output, each of the switching signals cs1 to cs3 includes one pulse that is turned on for a predetermined time Tona. Although the case has been described, it is not important how many pulses these switching signals cs1 to cs3 are formed, that is, how many pulses are output during the predetermined time Tona. Is set,
It is important that the pulse output time is set by the predetermined time Tona.

The number of switching pulses that are turned on during the predetermined time Tona is related to the motor torque pattern. When an appropriate torque pattern is determined according to the type of load, the determined torque is determined. The number of switching pulses can be determined according to the pattern.

[0031]

As described above, in the speed control method of the SR motor according to the present invention, PWM control is performed when the motor is in a transient state, and dwell control is performed when the motor is in a steady state. Because the switching frequency of the switching transistor is significantly reduced, no expensive power switching element is used, the price is reduced by using a general switching element, and the current applied to the motor winding is not rapidly increased. Therefore, there is an effect that a separate current protection circuit can be omitted.

Further, there is an effect that the switching frequency can be reduced, the switching loss can be reduced, and the efficiency of the motor can be improved. Further, there is an effect that the rotation angle of the motor can be predicted based on time by using a load such as a fan that operates at a constant speed for a long time.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a speed control method of an SR motor according to the present invention.

FIG. 2 is a graph showing a speed control pattern of the SR motor according to the present invention.

FIG. 3 is a waveform diagram showing a switching signal applied to the gate of a switching transistor when performing dwell control of the SR motor according to the present invention, wherein (a) is a waveform diagram when the motor is driven at a low speed, (b) is a waveform diagram when driving at a medium speed, and (c) is a waveform diagram when driving at a high speed.

FIG. 4 is a cross-sectional view showing the structure of a conventional three-phase SR motor.

FIG. 5 is a speed control circuit diagram of a conventional three-phase SR motor.

Fig. 6 When performing PWM voltage control of a conventional three-phase SR motor,
FIG. 4 is a waveform diagram of a signal output from each element and a current flowing through a winding.

FIG. 7 is a waveform diagram of a signal output from each element and a current flowing through a winding when current control of a conventional three-phase SR motor is performed.

[Explanation of symbols]

 21… Inverter 22… Detection sensor 23… Speed detector 24… Speed controller C… Capacitor Q1 ～ Q6… Switching transistor D1 ～ D6… Diode La, Lb, Lc… Motor winding

Claims (10)

[Claims] 1. A method for controlling the speed of a switched reluctance motor using a load having a large mechanical inertia, comprising controlling a pulse width modulation (PWM) of the motor after the switched reluctance motor is started. Increasing the speed, and based on the speed of the switched reluctance motor,
A step of determining whether the switched reluctance motor is in a steady state; and, when the switched reluctance motor is in a steady state or close to a steady state, the switching transistor of the inverter is switched for a preset time. Controlling the current flowing through the winding to be constant irrespective of a change in the load of the motor. 2. The switching reluctance motor according to claim 1, wherein a current speed of the switched reluctance motor is compared with a preset reference speed to determine whether the switched reluctance motor is in a steady state. Speed control method for switched reluctance motor. 3. The method according to claim 1, wherein the preset time is determined by a speed of the switched reluctance motor. 4. The speed control method for a switched reluctance motor according to claim 1, wherein the switching operation of the switching transistor is performed once or more at the preset time. 5. When the load of the switched reluctance motor is overloaded and the speed of the switched reluctance motor is lower than the preset speed,
Stop driving the switch reluctance motor,
The speed of the switched reluctance motor according to any one of claims 1 to 4, further comprising a step of controlling to have stability against overload without using a current sensor. Control method. 6. A detection sensor (22) for detecting rotation of a rotor of a motor, and a position of the rotor is determined based on a signal output from the detection sensor (22) to detect a detection pulse signal (ps).
And a plurality of switching signals (cs1 to cs6) based on the detected pulse signal (ps).
A) a speed control unit (24) that outputs a signal to each gate of the first to sixth switching transistors (Q1 to Q6) of the inverter (21), and a switched reluctance motor using a load with a large mechanical inertia. In the speed control method, after the switched reluctance motor is started, a step of performing pulse width modulation (PWM) control to increase the speed of the motor, and based on the speed of the switched reluctance motor,
A step of determining whether the switched reluctance motor is in a steady state; and, if the determination result indicates that the switched reluctance motor is in a steady state, after the detection pulse signal is input, the first A sixth switching transistor (Q1 to Q6) outputs an ON-state switching signal to any one of the switching transistors, and a switching transistor connected in series to the selected switching transistor has a predetermined period of time. Outputting a switching signal for maintaining the ON state, and controlling the current flowing through the windings of the motor connected to the two switching transistors to a constant value. Speed control method. 7. The switching reluctance motor according to claim 6, wherein a current speed of the switched reluctance motor is compared with a preset reference speed to determine whether the switched reluctance motor is in a steady state. Speed control method for switched reluctance motor. 8. The method according to claim 6, wherein the preset time is determined by a speed of the switched reluctance motor. 9. The switching operation of a switching transistor serially connected to any one of the selected switching transistors may be performed at a predetermined time.
The speed control method for a switched reluctance motor according to claim 6, wherein the method is performed once or more times. 10. When the load of the switched reluctance motor is overloaded and the speed of the switched reluctance motor falls below a predetermined speed, the driving of the switched reluctance motor is stopped, and 7. The speed control method for a switched reluctance motor according to claim 6, further comprising a step of performing control so as to have stability against overload without using a sensor.